A typical prior art head and disk system 10 is illustrated in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded. Historically the substrate was AIMg with an amorphous NiP surface film deposited by wet electroless plating. The AlMg/NiP disk was considered to be the substrate on which thin films were vacuum deposited to form the layers of the magnetic media.
One embodiment of the thin films 21 typically used with a glass substrate includes an amorphous initial thin film which is called a pre-seed layer and is followed by a crystalline seed layer. Typically both the pre-seed layer and seed layer are relatively thin layers. In U.S. Pat. No. 5,789,056 to Bian, et al., the use of a crystalline CrTi seed layer is described. Following the seed layer is typically a chromium or chromium alloy underlayer such as Cr, CrV and CrTi. One or more ferromagnetic layers based on various alloys of cobalt follow the underlayer. For example, a commonly used alloy is CoPtCr. Additional elements such as tantalum and boron are also often used in the magnetic alloy. A protective overcoat layer is used to improve wearability and corrosion resistance. The disk embodiment described above is one of many possibilities. For example, multiple seed layers, multiple underlayers and multiple magnetic layers have all been proposed in the prior art.
U.S. Pat. No. 6,593,009 issued to Bian, et al. on Jul. 15, 2003 describes a thin film magnetic media structure comprising a pre-seed layer CrTi which presents an amorphous or nanocrystalline structure. In the following text the term amorphous will be used to include nanocrystalline. The preferred seed layer is said to be RuAl. The use of the CrTi/RuAl bi-layer structure provides superior adhesion to the substrate and resistance to scratching, as well as, excellent coercivity and signal-to-noise ratio (SNR) and reduced cost over the prior art.
U.S. Pat. No. 6,567,236 to Doerner, et al., describes a preferred embodiment of a layer structure as: an amorphous pre-seed layer of CrTi, a seed layer of RuAl, a crystalline underlayer of CrTi, a bottom ferromagnetic layer of CoCr, an antiferromagnetic coupling/spacer layer of Ru; and a top ferromagnetic structure including: a thin first sublayer of CoCr, CoCrB or CoPtCrB, and a thicker second sublayer of CoPtCr with a lower moment than the first sublayer.
U.S. Pat. No. 5,879,783 to Chang, et al., describes the use of a NiP seed layer which is sputtered deposited on a glass or glass-ceramic substrate, and the surface is roughened by oxidation. In U.S. Pat. No. 6,596,419 to Chen, et al., a magnetic recording medium is described that includes a seed layer comprising a material selected from the group consisting of oxidized NiP (NiPOx) and CrTi. The thickness of the seed layer is said to be about 4 nm to 6 nm. It is stated that the CrTi and NiPOx seed layers enhance the development of CoTi/Cr(200) and Co(11.0) crystallographic orientation, and help to reduce grain size of CoTi/Cr-alloy underlayers.
The preferred orientation (PO) of the various crystalline materials forming the layers on the disk, as discussed herein, is not necessarily an exclusive orientation which may be found in the material, but is merely the most prominent orientation. When the Cr underlayer is sputter deposited at a sufficiently elevated temperature on a NiP-coated AIMg substrate a [200] PO is usually formed. This PO promotes the epitaxial growth of [11-20] PO of the hexagonal close-packed (hcp) cobalt (Co) alloy, and thereby improves the magnetic performance of the disk. The [11-20] PO refers to a film of hexagonal structure whose (11-20) planes are predominantly parallel to the surface of the film. Likewise the [10-10] PO refers to a film of hexagonal structure whose (10—10) planes are predominantly parallel to the surface of the film. The [10-10] PO can be epitaxially grown on an appropriate underlayer with a PO of [112].
One technique used in the prior art to improve magnetic recording performance on thin film disks is circumferential polishing to create a pattern of fine “scratches” (circumferential texture) which are generally oriented along tracks (concentric circles) on the disk surface. The scale of the texture of commercial thin film disks is microscopic with a peak-to-valley of less than 5 nm typically. A 5 nm texture appears mirror-like to the untrained eye. Special polishing equipment is necessary to achieve circumferential texture this fine. The topography of the surface on which a thin film is deposited can have a significant effect on the way the film nucleates and grows and also upon its characteristics. So called circumferential texture on magnetic disks has been commonly used to influence the inplane magnetic anisotropy for a wide range of magnetic alloys. For longitudinal recording it is sometimes useful to have a higher coercivity (Hc) and Mrt in the circumferential direction than in the radial direction. The ratio of the circumferential Hc to the radial Hc is called the coercivity orientation ratio (OR). Similarly the ratio of the circumferential Mrt to the radial Mrt is called the Mrt orientation ratio (OR). Current disks typically use hexagonal close packed (hcp) cobalt alloys and most (but not all) circumferentially textured disks have an Hc or Mrt OR>1.